Biosensors Detect Bacteria
The National Academy of Sciences announced a three-year, $271,930 grant to Rotello in July 2013 to develop and test his inkjet-printed, nanoparticle-based test strips with researchers at the Lahore University of Management Sciences (LUMS), Pakistan.
For this reason and more, a team of UMass Amherst students under the direction of Chemistry Professor Vincent Rotello are working on the Colorimetric Bacterial Sensing Project to place a paper strip capable of detecting the drinkability of water into the hands of the masses. And they are happy to do it. As lab chemists, they do plenty of general research and delight in finding ways to apply their work in real-life situations. “If you can come up with a good way to mass produce a test for water safety, you can make a huge difference,” Rotello says.
To the naked eye, the strips look like normal pieces of paper. But on a microscopic level, there’s an enzymatic party going on. The strips contain enzymes that are bound by nanoparticles. Enzymes are responsible for all of the body’s chemical processes; they are what make things happen. But in this case, the nanoparticles act as a stopper of the enzyme.
Nanoparticles, Rotello explains, are particles that are really, really small. The category applies to all structures between one and 100 nanometers. A 100-nanometer particle, for example, is 800 times smaller (in width) than a human hair.
“If you were to compare the size of my head to the planet Earth, that would be about the same comparison as a nanoparticle to my head,” Rotello says.
Because nanoparticles are so small, they are ideal for binding to biological compounds. So when the strip is placed in water, any bacteria that is present in the water starts to bind with the nanoparticles, removing them from the enzymes. As the enzymes are freed, they start to process, turning the strip a bright red color. This indicates that bacteria are present and the water is not drinkable.
The more bacteria, the brighter red the strip turns. When drinkable tap water is tested, the strip turns yellow instead. The strips can detect down to about 1,000 bacteria cells per milliliter, which Rotello says is a functional level for testing water in developing countries. “We’ve tested it in sort of real-world conditions and it seems to work pretty well,” Rotello said.
The chemistry students are working to bring the sensitivity level down to a degree that the strips can detect below US EPA standards. Currently, the strips can detect when the standards have been exceeded, yet cannot quite read bacterial levels that approach US EPA criteria for contamination. Even the most minor of contaminations poses risks to communities, especially children and the elderly.
And in the grand scheme of things, the strips are easy and inexpensive to produce; students are actually using an inkjet printer to make them. Taking regular ink cartridges, they remove the ink and replace it with the materials. Ink cartridges are equipped with four channels (more than enough for the necessary compounds), one for each color: cyan, magenta, yellow, and black. Students place the nanoparticles in one channel, the substrate in another, and the enzyme in a third in whatever ratio they need.
“It’s a really nice trick because if you think about it, the technology of inkjet printing is amazing. You can get such small droplet sizes and such fine detail,” Rotello says.
Brian Creran, 29, is a fourth-year graduate student and is leading the research related to the printing of the strips. Students are working to perfect the inkjet system, and Rotello estimates that the team soon will be ready to move on to bigger and better printers. After that, he plans to make use of a gravure printer, a high-quality long-running press on campus.
The project is still in the research stages and will move into the engineering stage within the year. One obstacle remains: designing the strip so it can withstand extreme conditions. In order for the strips to be functional in developing countries, they need to endure the “tough life” of transit. They must prove stable enough to bear extreme heat and humidity.
“We are working on some synthetic compounds to replace the natural ones; the natural ones are not so stable,” says Xiaoning Li, 25. Li is a fourth-year graduate student from China and has been working on the project since last year. Li moved here because she was attracted to the UMass Amherst Chemistry program and feels that it is paying off. “It helped me to think on how to move research in the lab towards real applications you can use,” Li says.
Rotello concurs that the University is working hard to create more connections between laboratory work and the manufacturing industry. “You’ve got this chasm between lab work and commercialization. If you could build a bridge over that, then you’re in good shape. That’s what we’re trying to do,” Rotello says. The connection of these two fields is also a goal of the Center for Hierarchical Manufacturing, an on-campus National Science Foundation Nanoscale Science and Engineering Center that is funding the sensor project.
Even undergraduates have hands in the research. Michael Gilbert, 21, is a senior-year chemistry student helping to move the project forward. Rotello attests to the value of the lab experience and is confident that it will help the students find jobs after graduation. “Having good research under your belt makes you very employable,” Rotello says.
Rotello and his student team will continue to perfect the formulation process until the biosensing strips work as well in the field as in the laboratory.
Amanda Drane ‘12